Stretched optical compensation film

ABSTRACT

Disclosed is a stretched optical compensation film which is a phase difference film containing a cellulose-based resin and having excellent optical properties. The stretched optical compensation film of the present invention contains 0.5 to 30 parts by mass of a β-diketone compound represented by Formula (I) with respect to 100 parts by mass of the cellulose-based resin. Positions R 1  and R 2  each independently represent an alkyl group having 1 to 20 carbon atoms which is optionally substituted, an arylalkyl group having 7 to 20 carbon atoms which is optionally substituted or an aryl group having 6 to 20 carbon atoms which is optionally substituted. Position R 3  represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.

TECHNICAL FIELD

The present invention relates to a stretched optical compensation film.More particularly, the present invention relates to a stretched opticalcompensation film in which, by incorporating a specificretardation-increasing agent into a cellulose-based resin,unprecedentedly large retardation is imparted and optical properties areimproved.

BACKGROUND ART

Conventionally, resin films such as cellulose acylate films,polycarbonate films and polyolefin films have been used as opticalcompensation films for liquid crystal displays. Thereamong, celluloseacylate films have been widely used since they have excellentcompatibility with polyvinyl alcohol used as a polarizer.

However, cellulose ester films themselves do not have sufficientretardation (birefringence) required for an optical compensation film;therefore, a variety of methods have been examined for imparting acellulose ester film with retardation. In addition, in recent years,increasingly large retardation has been demanded due to furtherexpansion of viewing angle and reduction in thickness of liquid crystaltelevisions.

For improvement of the retardation of a resin film, a method of adding aretardation-increasing agent is known; however, it has been difficult toapply such a method into practice since conventionalretardation-increasing agents are required to be added in a large amountand cause problems of bleed-out and the like. In addition, for example,a method of reducing the total acyl group-substitution degree ofcellulose has also been proposed; however, practical application of thismethod is also difficult since there are problems of an increase in themoisture absorption and the like.

Under such circumstances, as a step toward practical application,methods of adding a specific retardation-increasing agent have beenrecently proposed. For example, in Patent Document 1, a phase differenceplate which comprises a cellulose ester film containing a specificaromatic compound as a retardation-increasing agent is proposed.Furthermore, in Patent Document 2, a cellulose ester film in which apolycyclic aromatic compound having a phenolic hydroxyl group is used asa retardation-increasing agent is proposed. Meanwhile, in PatentDocument 3, an UV filter element in which dibenzoylmethane is used as anultraviolet absorber, not as a retardation-increasing agent, isproposed.

RELATED ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent No. 4605908

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. 2010-222433

Patent Document 3: Japanese Unexamined Patent Application PublicationNo. 2003-177235

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the cellulose ester film of Patent Document 1, which comprisesa retardation-increasing agent composed of a specific aromatic compound,does not have sufficient compatibility and, therefore, satisfactoryoptical property-improving effect is not attained. Furthermore, thecellulose ester film of Patent Document 2, in which a polycyclicaromatic compound having a phenolic hydroxyl group is used as aretardation-increasing agent, also does not have sufficientcompatibility and, therefore, satisfactory optical property-improvingeffect is not attained.

Meanwhile, the UV filter element of Patent Document 3 is nothing morethan a UV absorption-related technology and, in Patent Document 3, thereis absolutely no description with regard to the opticalproperty-improving effect exerted by the addition of dibenzoylmethane,let alone disclosure of application of the technology to a stretchedoptical compensation film.

In view of the above, an object of the present invention is to provide astretched optical compensation film that is a phase difference filmcomprising a cellulose-based resin and having excellent opticalproperties.

Means for Solving the Problems

In order to solve the above-described problems, the present inventorsintensively studied and discovered that the above-described object canbe achieved by a film obtained by blending a β-diketone compound in acellulose-based resin, thereby completing the present invention.

That is, the stretched optical compensation film of the presentinvention is characterized by comprising 0.5 to 30 parts by mass of aβ-diketone compound represented by the following Formula (I) withrespect to 100 parts by mass of a cellulose-based resin:

(wherein, R₁ and R₂ each independently represent an alkyl group having 1to 20 carbon atoms which is optionally substituted, an arylalkyl grouphaving 7 to 20 carbon atoms which is optionally substituted or an arylgroup having 6 to 20 carbon atoms which is optionally substituted; andR₃ represents a hydrogen atom or an alkyl group having 1 to 10 carbonatoms).

In the present invention, the term “excellent optical properties” meansthat the film is imparted with large retardation, and this retardationcan be generally understood in terms of the film in-plane retardationvalue (Ro) and the thickness-direction retardation value (Rth).

Here, the values of Ro and Rth are defined by the following equations,respectively.Ro=(nx−ny)×dRth={(nx+ny)/2−nz}×d

[wherein, nx represents the refractive index in the direction with thehighest film in-plane refractive index; ny represents the film in-planerefractive index in the direction perpendicular to the direction of nx;nz represents the refractive index in the film thickness direction; andd represents the film thickness (μm)]

These retardation values, Ro and Rth, can be measured by, for example,using an automatic birefringence meter such as KOBRA-WR (manufactured byOji Scientific Instruments) or RETS-100 (manufactured by OtsukaElectronics Co., Ltd.).

Effects of the Invention

The stretched optical compensation film of the present invention hasexcellent optical properties. That is, the stretched opticalcompensation film of the present invention is imparted with largeretardation and can thus be suitably used as a phase difference film ofliquid crystal displays, particularly VA-type liquid crystal displays inwhich a VA-mode liquid crystal cell is used.

MODE FOR CARRYING OUT THE INVENTION

The stretched optical film of the present invention will now bedescribed in detail.

The cellulose-based resin used in the present invention may be of anykind; however, it is preferably a lower fatty acid ester of cellulose.The term “lower fatty acid” in the lower fatty acid ester of cellulosemeans a fatty acid having not more than 6 carbon atoms and examples ofsuch lower fatty acid ester of cellulose include cellulose acetate,cellulose propionate and cellulose butyrate, as well as mixed fatty acidesters such as cellulose acetate propionate and cellulose acetatebutyrate that are described in, for example, Japanese Unexamined PatentApplication Publication Nos. H10-45804 and H8-231761 and U.S. Pat. No.2,319,052.

In the β-diketone compound used in the present invention, examples ofthe alkyl group having 1 to 20 carbon atoms which is optionallysubstituted and represented by R₁ and R₂ in the above-described Formula(I) include methyl, ethyl, propyl, isopropyl, butyl, isobutyl,sec-butyl, tert-butyl, amyl, isoamyl, hexyl, isohexyl, heptyl, octyl,isooctyl, tert-octyl, 2-ethylhexyl, nonyl, isononyl, decyl, undecyl,dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl,octadecyl, nonadecyl and icosyl. Further, examples of the arylalkylgroup having 7 to 20 carbon atoms which is optionally substituted andrepresented by R₁ and R₂ include benzyl, phenethyl,2-phenylpropane-2-yl, styryl, cinnamyl, diphenylmethyl andtriphenylmethyl. Moreover, examples of the aryl group which isoptionally substituted and represented by R₁ and R₂ include phenyl,naphthyl, phenanthryl and anthracenyl. Examples of substituent includealkyl groups having 1 to 10 carbon atoms, such as methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl, isoamyl, hexyl,isohexyl, heptyl, octyl, isooctyl, tert-octyl, 2-ethylhexyl, nonyl,isononyl and decyl; alkoxy groups having 1 to 10 carbon atoms, such asmethoxy, ethoxy, propoxy, isopropoxy, butoxy and isobutoxy; alkanoyloxygroups having 1 to 10 carbon atoms, such as methanoyloxy, ethanoyloxyand propanoyloxy; alkoxycarbonyl groups having 1 to 10 carbon atoms,such as methoxycarbonyl, ethoxycarbonyl and propoxycarbonyl;alkoxyalkyleneoxy groups having 2 to 20 carbon atoms, such asmethoxymethyleneoxy, ethoxymethyleneoxy and methoxyethyleneoxy;alkoxycarbonylalkyleneoxy groups having 3 to 21 carbon atoms, such asmethoxycarbonylmethyleneoxy, ethoxycarbonylmethyleneoxy andmethoxycarbonylethyleneoxy; halogen atoms such as chlorine and bromine;hydroxy group; and a —NR₄R₅ group (wherein, R₄ and R₅ each independentlyrepresent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms oran acyl group having 1 to 10 carbon atoms). Here, the above-describedalkoxyalkyleneoxy groups are specifically represented by the followingformula:

and the above-described alkoxycarbonylalkyleneoxy groups arespecifically represented by the following formula:

Examples of the alkyl group having 1 to 10 carbon atoms which isrepresented by R₃ in the above-described Formula (I) include methyl,ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl,isoamyl, hexyl, isohexyl, heptyl, octyl, isooctyl, tert-octyl,2-ethylhexyl, nonyl, isononyl and decyl.

Among these β-diketone compounds, compounds in which at least either oneof R₁ and R₂ in the above-described Formula (I) is an aryl group that isoptionally substituted, particularly those compounds represented by thefollowing Formula (I-1) are preferred because they have excellentcompatibility with cellulose acylate and are capable of imparting goodretardation:

(wherein, X₁ to X₁₀ each independently represent a hydrogen atom, ahydroxy group, a halogen atom, an alkyl group having 1 to 10 carbonatoms, an alkoxy group having 1 to 10 carbon atoms, an alkanoyloxy grouphaving 1 to 10 carbon atoms, an alkoxycarbonyl group having 1 to 10carbon atoms, an alkoxyalkyleneoxy group having 2 to 20 carbon atoms, analkoxycarbonylalkyleneoxy group having 3 to 21 carbon atoms, a phenylgroup or a —NR₄R₅ group (wherein, R₄ and R₅ each independently representa hydrogen atom, an alkyl group having 1 to 10 carbon atoms or an acylgroup having 1 to 10 carbon atoms); and at least one pair of X₁ and X₂,X₂ and X₃, X₄ and X₅, X₆ and X₇, X₇ and X₈, X₈ and X₉, and X₉ and X₁₀optionally form a benzene ring together).

In the above-described Formula (I-1), examples of the alkyl group having1 to 10 carbon atoms which is represented by X₁ to X₁₀ include methyl,ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl,isoamyl, hexyl, isohexyl, heptyl, octyl, isooctyl, tert-octyl,2-ethylhexyl, nonyl, isononyl and decyl, and examples of the alkoxygroup having 1 to 10 carbon atoms include methoxy, ethoxy, propoxy,isopropoxy, butoxy and isobutoxy. Further, examples of the alkanoyloxygroup having 1 to 10 carbon atoms include methanoyloxy, ethanoyloxy andpropanoyloxy, and examples of the alkoxycarbonyl group having 1 to 10carbon atoms include methoxycarbonyl, ethoxycarbonyl andpropoxycarbonyl. Still further, examples of the alkoxyalkyleneoxy grouphaving 2 to 20 carbon atoms include methoxymethyleneoxy,ethoxymethyleneoxy and methoxyethyleneoxy, and examples of thealkoxycarbonylalkyleneoxy group having 3 to 21 carbon atoms includemethoxycarbonylmethyleneoxy, ethoxycarbonylmethyleneoxy andmethoxycarbonylethyleneoxy.

Examples of the alkyl group having 1 to 10 carbon atoms which may berepresented by the above-described R₄ and R₅ include the same ones asthose described above. Further, examples of the acyl group having 1 to10 carbon atoms which may be represented by the above-described R₄ andR₅ include methanoyl (formyl), ethanoyl(acetyl), propanoyl, butanoyl,pentanoyl, hexanoyl, octanoyl and nonanoyl groups.

Examples of the β-diketone compound used in the present invention areshown below; however, the present invention is not restricted thereto.

These β-diketone compounds are used in an amount of 0.5 to 30 parts bymass, preferably 1 to 20 parts by mass, with respect to 100 parts bymass of a cellulose-based resin. When the amount of a β-diketonecompound is less than 0.5 parts by mass, its effect cannot besufficiently exhibited, while when the amount exceeds 30 parts by mass,bleeding occurs and the physical properties of the resulting stretchedoptical compensation film are deteriorated; therefore, such amount of aβ-diketone compound is not preferred.

In the stretched optical compensation film of the present invention, aplasticizer can be arbitrarily used. Examples of the plasticizer includephthalate-based plasticizers such as dibutyl phthalate, butylhexylphthalate, diheptyl phthalate, dioctyl phthalate, diisononyl phthalate,diisodecyl phthalate, dilauryl phthalate, dicyclohexyl phthalate anddioctyl terephthalate; adipate-based plasticizers such as dioctyladipate, diisononyl adipate, diisodecyl adipate anddi(butyldiglycol)adipate; phosphate-based plasticizers such as triphenylphosphate, tricresyl phosphate, trixylenyl phosphate,tri(isopropylphenyl)phosphate, triethyl phosphate, tributyl phosphate,trioctyl phosphate, tri(butoxyethyl)phosphate and octyldiphenylphosphate; polyester-based plasticizers in which ethylene glycol,diethylene glycol, triethylene glycol, 1,2-propylene glycol,1,3-propylene glycol, 1,3-butane diol, 1,4-butane diol, 1,5-hexane diol,1,6-hexane diol, neopentyl glycol or the like is used as a polyhydricalcohol, oxalic acid, malonic acid, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalicacid, isophthalic acid, terephthalic acid or the like is used as adibasic acid and, as required, a monohydric alcohol or a monocarboxylicacid (such as acetic acid or aromatic acid) is used as a stopper;tetrahydrophthalic acid-based plasticizers; azelaic acid-basedplasticizers; sebacic acid-based plasticizers; stearic acid-basedplasticizers; citric acid-based plasticizers; trimellitic acid-basedplasticizers; pyromellitic acid-based plasticizers; biphenylenepolycarboxylic acid-based plasticizers; and polyhydric alcohol aromaticacid ester-based plasticizers (such as trimethylolpropane tribenzoate).

Further, in the stretched optical compensation film of the presentinvention, a variety of other additives, such as a phosphorus-based,phenol-based or sulfur-based antioxidant, an ultraviolet absorber and ahindered amine-based light stabilizer, may also be incorporated.

Examples of the above-described phosphorus-based antioxidant includetriphenyl phosphite, tris(2,4-di-tert-butylphenyl)phosphite,tris(nonylphenyl)phosphite, tris(dinonylphenyl)phosphite, tris(mono-,di-mixed nonylphenyl)phosphite,bis(2-tert-butyl-4,6-dimethylphenyl)•ethyl phosphite, diphenyl acidphosphite, 2,2′-methylene-bis(4,6-di-tert-butylphenyl)octyl phosphite,diphenyldecyl phosphite, phenyldiisodecyl phosphite, tributyl phosphite,tris(2-ethylhexyl)phosphite, tridecyl phosphite, trilauryl phosphite,dibutyl acid phosphite, dilauryl acid phosphite, trilauryltrithiophosphite, bis(neopentyl glycol)•1,4-cyclohexane dimethyldiphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite,bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite,distearylpentaerythritol diphosphite, phenyl-4,4′-isopropylidenediphenol•pentaerythritol diphosphite, tetra(C12-15 mixedalkyl)-4,4′-isopropylidene diphenyl phosphite,bis[2,2′-methylene-bis(4,6-diamylphenyl)]•isopropylidene diphenylphosphite, hydrogenated-4,4′-isopropylidene diphenol polyphosphite,bis(octylphenyl)•bis[4,4′-n-butylidene-bis(2-tert-butyl-5-methylphenol)]•1,6-hexanediol•diphosphite,tetratridecyl•4,4′-butylidene-bis(2-tert-butyl-5-methylphenol)diphosphite,hexa(tridecyl)•1,1,3-tris(2-methyl-5-tert-butyl-4-hydroxyphenyl)butane•triphosphonite,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and2-butyl-2-ethylpropane diol•2,4,6-tri-tert-butylphenol monophosphite.

Examples of the above-described phenol-based antioxidant include2,6-di-tert-butyl-p-cresol, 2,6-diphenyl-4-octadesiloxyphenol,stearyl(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,distearyl(3,5-di-tert-butyl-4-hydroxybenzyl)phosphonate,tridecyl•3,5-di-tert-butyl-4-hydroxybenzyl thioacetate,thiodiethylene-bis[(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],4,4′-thiobis(6-tert-butyl-m-cresol),2-octylthio-4,6-di(3,5-di-tert-butyl-4-hydroxyphenoxy)-s-triazine,2,2′-methylene-bis(4-methyl-6-tert-butylphenol),bis[3,3-bis(4-hydroxy-3-tert-butylphenyl)butyric acid]glycol ester,4,4′-butylidene-bis(4,6-di-tert-butylphenol),2,2′-ethylidene-bis(4,6-di-tert-butylphenol),1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,bis[2-tert-butyl-4-methyl-6-(2-hydroxy-3-tert-butyl-5-methylbenzyl)phenyl]terephthalate,1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate,1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate,1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-2,4,6-trimethylbenzene,1,3,5-tris[(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate,tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane,2-tert-butyl-4-methyl-6-(2-acryloyloxy-3-tert-butyl-5-methylbenzyl)phenol,3,9-bis[2-(3-tert-butyl-4-hydroxy-5-methylhydrocinnamoyloxy)-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane]and triethyleneglycol-bis[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate].

Examples of the above-described sulfur-based antioxidant include dialkylthiodipropionates such as dilauryl thiodipropionate, dimyristylthiodipropionate, myristylstearyl thiodipropionate and distearylthiodipropionate; and β-alkylmercaptopropionates of polyols, such aspentaerythritol tetra(β-dodecylmercaptopropionate).

Examples of the above-described ultraviolet absorber include 2-hydroxybenzophenones such as 2,4-dihydroxybenzophenone,2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone,2-hydroxy-4-tert-butyl-4′-(2-methacryloyloxyethoxyethoxy)benzophenoneand 5,5′-methylene-bis(2-hydroxy-4-methoxybenzophenone);2-(2-hydroxyphenyl)benzotriazoles such as2-(2-hydroxy-5-methylphenyl)benzotriazole,2-(2-hydroxy-5-tert-octylphenyl)benzotriazole,2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3-dodecyl-5-methylphenyl)benzotriazole,2-(2-hydroxy-3-tert-butyl-5-C7 to C9mixed-alkoxycarbonylethylphenyl)triazole,2-(2-hydroxy-3,5-dicumylphenyl)benzotriazole,2,2′-methylene-bis(4-tert-octyl-6-benzotriazolylphenol) and polyethyleneglycol ester of 2-(2-hydroxy-3-tert-butyl-5-carboxyphenyl)benzotriazole;2-(2-hydroxyphenyl)-1,3,5-triazines such as2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyl-1,3,5-triazine,2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine,2-(2-hydroxy-4-octoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazineand2-(2-hydroxy-4-acryloyloxyethoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine;benzoates such as phenyl salicylate, resorcinol monobenzoate,2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate,2,4-di-tert-amylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate andhexadecyl-3,5-di-tert-butyl-4-hydroxybenzoate; substituted oxanilidessuch as 2-ethyl-2′-ethoxyoxanilide and 2-ethoxy-4′-dodecyloxanilide; andcyanoacrylates such as ethyl-α-cyano-β,β-diphenylacrylate andmethyl-2-cyano-3-methyl-3-(p-methoxyphenyl)acrylate.

Examples of the above-described hindered amine-based light stabilizerinclude 2,2,6,6-tetramethyl-4-piperidyl stearate,1,2,2,6,6-pentamethyl-4-piperidyl stearate,2,2,6,6-tetramethyl-4-piperidylbenzoate,bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate,bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidyl)sebacate,tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate,tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate,bis(2,2,6,6-tetramethyl-4-piperidyl)•bis(tridecyl)-1,2,3,4-butanetetracarboxylate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)•bis(tridecyl)-1,2,3,4-butanetetracarboxylate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)-2-butyl-2-(3,5-ditert-butyl-4-hydroxybenzyl)malonate,1-(2-hydroxyethyl)-2,2,6,6-tetramethyl-4-piperidinol/diethyl succinatepolycondensate,1,6-bis(2,2,6,6-tetramethyl-4-piperidylamino)hexane/dibromoethanepolycondensate,1,6-bis(2,2,6,6-tetramethyl-4-piperidylamino)hexane/2,4-dichloro-6-morpholino-s-triazinepolycondensate,1,6-bis(2,2,6,6-tetramethyl-4-piperidylamino)hexane/2,4-dichloro-6-tert-octylamino-s-triazinepolycondensate,1,5,8,12-tetrakis[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazine-6-yl]-1,5,8,12-tetraazadodecane,1,5,8,12-tetrakis[2,4-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-s-triazine-6-yl]-1,5,8,12-tetraazadodecane,1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino-s-triazine-6-ylamino]undecane,1,6,11-tris[2,4-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino-s-triazine-6-ylamino]undecane,3,9-bis[1,1-dimethyl-2-{tris(2,2,6,6-tetramethyl-4-piperidyloxycarbonyloxy)butylcarbonyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecaneand3,9-bis[1,1-dimethyl-2-{tris(1,2,2,6,6-pentamethyl-4-piperidyloxycarbonyloxy)butylcarbonyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane.

In addition to the above, in the stretched optical compensation film ofthe present invention, as required, other additives such as a filler, acoloring agent, a cross-linking agent, an antistatic agent, a plate-outinhibitor, a surface treatment agent, a lubricant, a flame retardant, afluorescent agent, an antifungal agent, an antibacterial agent, a metalinactivator, a mold-releasing agent, a pigment, a processing aid, anantioxidant, a light stabilizer and a foaming agent may also beincorporated.

A method of producing the stretched optical compensation film of thepresent invention will now be described; however the present inventionis not restricted thereto.

The stretched optical compensation film of the present invention isproduced by applying and drying a dope solution in which a celluloseester is dissolved in a solvent. A variety of additives can be alsoadded to the dope solution as required. In the dope solution, a higherconcentration of the cellulose ester is more preferred because thedrying load after flow-casting the dope solution onto a substrate can bereduced; however, when the concentration of the cellulose ester isexcessively high, the filtering load is increased, which results in poorfiltration accuracy. In order to attain reduction in both the dryingload and filtering load, the concentration of the cellulose ester ispreferably 10 to 30% by mass, more preferably 15 to 25% by mass.

The solvent used for preparing the dope solution of the presentinvention may be used individually or in combination with other solvent;however, from the standpoint of the production efficiency, it ispreferred to use a mixture of a good solvent and poor solvent ofcellulose ester. The mixing ratio of the good solvent and poor solventis preferably in the range of 70 to 98% by mass of the good solvent and30 to 2% by mass of the poor solvent. With regard to the good solventand poor solvent that are used in the present invention, a solvent whichindependently dissolves the cellulose ester used is defined as “goodsolvent” and a solvent which, by itself, only swells the cellulose esteror cannot dissolve the cellulose ester is defined as “poor solvent”.Therefore, the good and poor solvents are variable depending on theaverage acetylation degree of cellulose. For example, acetone is a goodsolvent for a cellulose ester having an average acetylation degree of55%; however, it is a poor solvent for a cellulose ester having anaverage acetylation degree of 60%. In this manner, the good and poorsolvents are not unambiguously determined in all cases. In the case ofcellulose triacetate which is a preferred cellulose ester in the presentinvention, the good solvent are, for example, organic halogen compoundssuch as methylene chloride and dioxolanes and, in the case of celluloseacetate propionate, the good solvents are, for example, methylenechloride, acetone and methyl acetate. Meanwhile, examples of the poorsolvent in these cases include methanol, ethanol, n-butanol, cyclohexaneand cyclohexanone.

As a method of dissolving a cellulose ester in the preparation of theabove-described dope solution, any conventional method can be employed;however, it is preferred to employ a method in which a cellulose esteris dissolved with stirring under pressure by heating in a temperaturerange which is not lower than the boiling point of the solvent undernormal pressure and where the solvent does not boil, because such amethod can inhibit generation of an aggregated undissolved matter called“gel” or “lump”. Alternatively, a method in which a cellulose ester ismixed with a poor solvent to wet or swell the cellulose ester and thendissolved by further mixing with a good solvent may also be preferablyemployed. Further, a known cooling dissolution method may be employed aswell. In cases where a cooling dissolution method is employed, methylacetate or acetone can be used as the good solvent. Pressurization canbe performed by a method of injecting an inert gas such as nitrogen gasor by increasing the vapor pressure of the solvent by heating. Theheating is preferably performed externally and, for example, ajacket-type heater is preferably employed because the temperature can beeasily controlled.

From the standpoint of the solubility of cellulose esters, heating afterthe addition of solvent is preferably performed in a temperature rangewhich is not lower than the boiling point of the used solvent undernormal pressure and where the solvent does not boil. When the heatingtemperature is excessively high, the required pressure is increased,which leads to a reduction in the productivity. The heating temperatureis preferably in the range of 45 to 120° C., more preferably 60 to 110°C., still more preferably 70 to 105° C. Further, the pressure isadjusted such that the solvent does not boil at the preset temperature.After the heating, the resulting cellulose ester solution is filteredthrough an appropriate filter medium such as a filter paper. As thefilter medium, a filter having a small absolute filtration accuracy ispreferred for removal of undesired matters and the like; however, anexcessively small absolute filtration accuracy leads to a problem thatclogging of the filter medium is likely to occur. Accordingly, theabsolute filtration accuracy of the filter medium is preferably 0.008 mmor less, more preferably in the range of 0.001 to 0.008 mm, still morepreferably in the range of 0.003 to 0.006 mm. The material of the filtermedium is not particularly restricted and any conventional filter mediumcan be used; however, filter media made of a plastic such aspolypropylene or Teflon (registered trademark) and those made of a metalsuch as stainless metal are preferred because these filter media arefree of problems such as fiber fall-off.

The filtration of the dope solution can be performed by a conventionalmethod; however, it is preferred to employ a method in which the dopesolution is filtered under pressure with heating in a temperature rangewhich is not lower than the boiling point of the solvent under normalpressure and where the solvent does not boil, because such a methodcauses only a small increase in the difference between the pressures oneach side of the filter medium (hereinafter, may be referred to as“filtration pressure”). The filtration temperature is preferably 45 to120° C., more preferably 45 to 70° C., still more preferably 45 to 55°C. The smaller the filtration pressure, the more preferred it is. Thefiltration pressure is preferably 1.6×10⁶ Pa or less, more preferably1.2×10⁶ Pa or less, still more preferably 1.0×10⁶ Pa or less.

As the substrate used in the flow-casting (casting) step, an endlessbelt-form or drum-form mirror-finished stainless-steel substrate ispreferred. The temperature of the substrate in the casting step ispreferably 0° C. to lower than the boiling point of the solvent. Thehigher the temperature, a higher temperature leads to a faster dryingrate; however, an excessively high temperature may cause foaming anddeterioration in the planarity of the resulting film. The substratetemperature is preferably 0 to 50° C., more preferably 5 to 30° C. Themethod of controlling the substrate temperature is not particularlyrestricted, and examples thereof include a method in which warm air orcool air is blown against the substrate and a method in which awarm-water vat is brought into contact with the substrate. Among thesemethods, a method of using a warm-water vat is preferred because heat isefficiently transferred and the time required for bringing the substrateto a constant temperature is shortened. When warm air is used, it isrequired that the temperature thereof be higher than the intendedtemperature of the substrate. In order to obtain a cellulose ester filmhaving good planarity, the amount of residual solvent at the time ofremoving the film from the substrate is preferably 10 to 120% by mass,more preferably 20 to 40% by mass or 60 to 120% by mass, particularlypreferably 20 to 30% by mass or 70 to 115% by mass.

In the present invention, the amount of residual solvent is defined bythe following equation:Amount of residual solvent=[(Film mass before heat treatment−Film massafter heat treatment)/(Film mass after heat treatment)]×100(%)

Here, the “heat treatment” performed at the time of measuring the amountof residual solvent refers to 1-hour heating of the film at 115° C.Further, in the step of drying the resulting cellulose ester film, thefilm detached from the substrate is further dried such that the amountof the residual solvent becomes preferably 3% by mass or less, morepreferably 0.5% by mass or less. In the film drying step, generally, amethod in which the film is dried while being transferred by a rollsuspension method or tenter method can be employed.

It is preferred that maintenance of the film width or stretching of thefilm be performed by a tenter method while a large amount of solventstill remains immediately after the film is detached from the substrate,because this allows superior dimensional stability-improving effect tobe exhibited. The means for drying the film is not particularlyrestricted and the film can be dried using, for example, hot air,infrared radiation, heated roll or microwave. From the standpoint ofsimplicity, the film is preferably dried using hot air. In this case, itis preferred that the drying temperature be stepwisely increased in therange of 40 to 150° C. and, in order to improve the dimensionalstability, it is more preferred that the film be dried at a temperatureof 50 to 140° C.

With regard to the thickness of the stretched optical compensation film,the thinner the film, the more preferred it is, because reduction in thethickness of a liquid crystal display can be more easily achieved;however, an excessively thin stretched optical compensation film causesan increase in the moisture permeability, which leads to insufficienttearing strength and the like. In order to attain low moisturepermeability as well as sufficient tearing strength and the like, thethickness of the cellulose ester film is preferably 10 to 150 μM, morepreferably 20 to 100 μm.

EXAMPLES

The stretched optical compensation film of the present invention willnow be described in more detail by way of examples thereof; however, thepresent invention is not restricted thereto.

Examples 1 to 9 and Comparative Example

In a mixed solvent composed of 400 parts by mass of methylene chlorideand 100 parts by mass of methyl alcohol, 100 parts by mass of cellulosetriacetate (acetylation degree: 61.5%, polymerization degree: 260) andthe respective additives shown in Table 1 below in the amount (parts bymass) shown in the same Table 1 were uniformly dissolved with stirringto prepare various dope solutions. Then, the thus obtained dopesolutions were each flow-casted on a glass plate to a thickness of about0.1 mm and dried at room temperature for 16 hours, followed by 1-hourdrying at 50° C. and 1-hour drying at 120° C. Thereafter, the resultantswere each uniaxially stretched at 150° C. using a stretching apparatusEX10-B1 (manufactured by Toyo Seiki Seisaku-sho, Ltd.), therebyobtaining various evaluation films. All of the thus obtained films had athickness of about 80 μm and were stretched at a draw ratio of 1.3times.

(Method of Evaluating Bleed Resistance)

The thus obtained films were each cut into a size of 30 mm×40 mm andleft to stand for 120 hours in an incubator at a temperature of 85° C.and a relative humidity of 90%. Then, the surface of each film wasvisually observed and the presence or absence of bleeding was verifiedbased on the following evaluation criteria.

∘: No bleeding was observed.

x: Bleeding was observed.

(Method of Measuring Retardation)

For the thus obtained films, using an automatic birefringence meterRETS-100 (manufactured by Otsuka Electronics Co., Ltd.), the in-planeretardation (Ro) and thickness-direction retardation (Rth) at awavelength of 590 nm were determined under an environment of 25° C. and60% RH in accordance with the following equations.Ro=(nx−ny)×dRth={(nx+ny)/2−nz}×d

[wherein, nx represents the refractive index in the direction with thehighest film in-plane refractive index; ny represents the film in-planerefractive index in the direction perpendicular to the direction of nx;nz represents the refractive index in the film thickness direction; andd represents the film thickness (μm)]

The thus obtained evaluation results are shown in Table 1 below.

TABLE 1 Added amount Bleed Retardation Additive (parts by mass)resistance Ro (nm) Rth (nm) Example 1 BD-1 10 ∘ 69 245 Example 2 BD-1 5∘ 26 156 Example 3 BD-2 10 ∘ 62 218 Example 4 BD-2 5 ∘ 31 168 Example 5BD-3 5 ∘ 50 260 Example 6 BD-4 5 ∘ 26 190 TPP* 5 Example 7 BD-4 1 ∘ 1078 TPP 9 Example 8 BD-5 5 ∘ 16 91 Example 9 BD-9 5 ∘ 26 120 ComparativeTPP* 10 ∘ 1 34 Example *triphenyl phosphate

As clearly seen from Table 1, in all of Examples where the β-diketonecompound according to the present invention was used, excellentcompatibility was attained. In addition, it is seen that, as compared tothe film of Comparative Example in which a general-purpose modifier,triphenyl phosphate, was used, the films of Examples showed superioroptical properties with larger retardation values (Ro and Rth).Furthermore, from the results of Examples 6 and 7, it is seen thatcomparable improving effect can be attained even when the β-diketonecompound according to the present invention and triphenyl phosphate aremixed.

The invention claimed is:
 1. A stretched optical compensation filmcomprising 0.5 to 30 parts by mass of a β-diketone compound representedby the following Formula (I) with respect to 100 parts by mass of acellulose-based resin:

wherein, R₁ and R₂ each independently represent an alkyl group having 1to 20 carbon atoms which is optionally substituted, an arylalkyl grouphaving 7 to 20 carbon atoms which is optionally substituted or an arylgroup having 6 to 20 carbon atoms which is optionally substituted; R₃represents a hydrogen atom or an alkyl group having 1 to 10 carbonatoms; and at least one of R₁ and R₂ represents an alkyl group.
 2. Thestretched optical compensation film according to claim 1, wherein saidβ-diketone compound is a compound in which, in said Formula (I), one ofR₁ and R₂ is an aryl group that is optionally substituted.
 3. Thestretched optical compensation film according to claim 2, wherein saidcellulose-based resin is cellulose acylate.
 4. The stretched opticalcompensation film according to claim 2, wherein said β-diketone compoundis a compound in which, in said Formula (I), the R₁ or R₂ that is notthe aryl group is a methyl group.
 5. The stretched optical compensationfilm according to claim 1, wherein said cellulose-based resin iscellulose acylate.
 6. The stretched optical compensation film accordingto claim 1, wherein the β-diketone compound is


7. The stretched optical compensation film according to claim 6, whereinsaid cellulose-based resin is cellulose acylate.